TXSquirrel

I thought BK already answered your questions? The issue with ATS is that you need to do a pull to push conversion plus finding a dual mass flywheel, so I guess you good with both hurdles?

Any used stock turbos and ECU you can find are likely not in working condition even if the seller claims they are. So I say go with Link because you should be able to get a stock tune from Link. Then find a pair of used stock turbos and have them rebuild, but that may end up costing more than simply buying a pair of new Garrett -7. But either way you can recover some money by selling the Garrett -5 and mystery HKS.

Yes the Link is a good option no matter which turbo you end up. With the -5 it will be more involved than just injectors and pump. As others mentioned you also need new sensors to measure air flow, either MAP or MAF. There are many fuel pumps available, but figuring out how you want to setup the wiring to supply the pump is another level of headache. You can find plenty of discussion on that here.

The tuner who told you GT2860R has fast spool on low boost was referring to -7. Both -5 and -7 are GT2860R, but they are at the opposite end of capacity. If the HKS that came off have no shaft play nor oil leak, why not put them back on? A pair of HKS oil restrictor cost little. Perhaps send an email to HKS, if lucky they may be able to decipher the part number. If they are really the GT25 series, then they are the streetable turbo you are looking for.

There are 2 different GT2860R, do you know which one you have? Or a part number?

Yeah but how different can it be, maybe 100°C vs 105°C? This is a viscous fan we're talking about, I mean how accurate can that be to begin with?

If you dig deeper, you can find interchangeable Nissan OEM fan clutch from other models. Those will be much cheaper and still available from any local Nissan dealer. I have not looked into R34, but I know the older Nissan Pathfinder/Xterra/Frontier fan clutch fits R32 perfectly and runs about ~$170 USD.

Was the run with HKS done on the same engine as Garrett?

I have the older 68mm Tomei elbows and ported stock manifolds. I am thinking about getting the cast Tomei manifolds, any thoughts on those? Because so far I have seen inconsistent results.

Yes to do it properly for how much? Custom piping and split design intercooler, a few thousand dollars? And to gain how much extra, 20whp? Tell me straight up you will personally spend money and get that setup done. A divided charge pipe cost $200 and gain 10whp. Actually even if it doesn't gain anything they can have my $200. Oh wait, I did already, because there are worse ways to waste $200.

https://www.gtrusablog.com/2018/04/split-twin-turbo-pipes-by-alex.html https://www.gtrusablog.com/2013/01/divided-rb26-twin-turbo-pipe.html Cheap mod, doesn't hurt to try

It's on e85, maybe max out injector or fuel pump

With Vcam peak power is at 6k, so that will be a change of driving/shifting habits.

Perhaps you can reach out to this person?

Sounds like new aftermarket exhaust and a set of proper Michelins and it's all set.